Thrombin is a mitogen for normal chick embryo fibroblasts but not for cells infected with the Rous Sarcoma Virus (RSV). We wish to determine whether thrombin binds specifically to normal cells and to determine whether there is a loss in binding capacity with the transformed cells. The wheat germ system is capable of translating eukaryotic messenger RNA with great efficiency and with very little extraneous background. We are isolating RNA from transforming and nontransforming Rous virus and will prepare proteins from them. We wish to determine whether there is an additional peptide fragment in the case of the Rous transforming virus that could account for its transforming properties.